This invention relates to propellers and more particularly to controllable pitch propellers which can function efficiently in four modes: forward thrust, reverse thrust, neutral, and power generation.
Auxiliary propulsive power on sailboats typically is provided via an inboard or outboard mounted engine/motor which develops thrust by means of a shaft mounted propeller interacting with the water. The simple propeller has the blades fixed to the hub and creates forward or reverse thrust by virtue of shaft rotation direction. The simple propeller has an undesirably high drag when sailing only and such drag can be mitigated by allowing the propeller to freely spin or, in the case of a two-bladed propeller, the blades may be "hidden" behind the keel or other appendage.
To accomplish the sailing-only mode with the drive shaft essentially stopped, propellers created for low drag typically either allow the blades to fold back when sailing to present a small profile to the oncoming fluid, or allow the blades to take a "feathered" position approximately parallel to fluid flow to minimize interference with the oncoming fluid. Both of these approaches must also incorporate a feature to provide reverse thrust, either by some remote mechanism or by self-adjustment, to position the blades in the extended position or in a reverse pitch (negative angle of attack) position. These propellers are relatively inefficient in the reverse mode if cambered blade sections are employed to maximize forward thrust. Alternatively, if flat, non-cambered blade sections are employed, forward and reverse thrust are equally powerful yet not optimally efficient.
None of the above propeller types have been designed for, or employed as, a power turbine to extricate rotary power from the flow of fluid. While there are devices to perform the turbine-type function, from instrument-level power of anemometer-type devices to towed impellers coupled to small generators, they are not designed also for main propulsion and maneuvering.
The present invention provides the capability of propulsion, maneuvering (reversing), power generation and low drag from a single efficient hydrodynamic device. Such a capability provides a wide range of applications for the boating industry and is of particular importance with the renewed interest in electric powered watercraft and the extensive array of electronic devices available to the boater.
Previous apparatus related to controllably varying propeller blade pitch positions are described in the following U.S. Pat. Nos. 629,966 to Otto; 813,074 to Barber; 1,055,455 to Esson; 1,520,746 to Boyce et al; 1,765,091 to Morris; 2,010,640 to Michl; 2,200,952 to Farrell; 2,246,539 to Ruths et al.; 2,290,666 to Ashelman et al.; 2,850,106 to Swan; 2,931,443 to Pehrsson; 2,955,659 to Daley; 2,988,156 to Coleman; 3,145,780 to Kean; 3,204,702 to Brown; 3,231,023 to Marshall; 3,295,610 to Frias; 3,497,306 to Phillips; 4,047,841 to Laurin; 4,140,434 to Bianchi; 4,231,317 to Brandt et al.; 4,693,671 to Thornton, Jr. et al.; and 4,929,153, 5,032,057, 5,129,785, and 5,326,223, all to Speer.
Of this prior art, U.S. Pat. No. 1,765,091 to Morris describes an arrangement which functions as self-activating, or "automatic" to vary the propeller blade pitch. The Morris design is configured specifically for an aircraft propeller and, as embodied, employs springs to fine tune blade pitch within less than a 90 degree range. Thus, unlike the present invention, the Morris construction does not allow total reversal of blade camber, i.e., rotating the blade pitch at least 180 degrees.
In U.S. Pat. No. 4,047,841 to Laurin, there is disclosed a propeller which varies blade pressure distribution depending on the function to be performed by the propeller. However, the Laurin propeller has its blade section optimized with only one edge as the leading edge and therefore is incapable of efficiently using either edge as the leading edge.
In U.S. Pat. No. 4,140,434 to Bianchi, there is disclosed a propeller constructed to operate in the forward, reverse, and feathering mode, but which is not capable of operating efficiently as a turbine, or power generator. The Bianchi propeller also has its blade section optimized with only one edge as the leading edge, thereby suffering from the same shortcomings as Laurin. Additionally, the nominal pitch adjustments of Bianchi employ an extra gear set in contrast to the present invention.
None of the above patents describes the controllable pitch propeller of the present invention wherein a cambered blade section is configured and positioned in the correct orientation for all modes of operation including a turbine, or power generating, mode.
It is thus one object of the present invention to provide a self-adjusting propeller device capable of selectively transmitting forces in either axial direction during use.
It is another object of the present invention to provide a device having minimal drag when not in use by self-adjustment of the blade pitch to pivot the blades to a minimal drag position, such as parallel to fluid flow.
It is a further object of the present invention to provide a minimal drag device which is highly efficient providing reverse as well as forward thrust.
It is yet another object of the present invention to provide a device capable of self-adjustment to act as an efficient turbine capable of taking rotary power from the passing fluid.
It is another object of the present invention to provide a device having a minimal number of parts and being relatively inexpensive to manufacture.
It is still another object of the present invention to provide a device whose construction provides ready interchangeability by means of the same shaft mounting as employed by conventional marine propellers or propulsors.
It is a further object of the present invention to provide a construction which is virtually maintenance free when operated in the manner intended.
It is yet another object of the present invention to provide a construction which can be "factory set" to achieve the best performance for each of a variety of specific applications, i.e., high-versus-low boat drag and particular shaft rotational speeds.
It is another object of the present invention to provide a self-adjusting propeller device which operates smoothly without inherent vibration or blade flutter.
It is still another object of the present invention to provide a self-adjusting propeller device whose hub is of minimal cross-section thus contributing to high overall efficiency of the device.
The present invention is a variation from mechanical controllable pitch configurations known as automatic variable propeller pitch devices. The following discussion identifies the functional particulars of the present invention.
The blade pitch of the present invention is concerned primarily with the "nominal" pitch, or orientation of the blade with respect to the drive shaft line, i.e., hub. Blades typically are helical in form with pitch varying from hub to tip in an efficient hydrodynamic manner. This invention provides for a cambered blade section form to be in the correct orientation, or sense, for all modes of operation. That is, the blade is designed to act efficiently regardless of which edge the fluid flow encounters first. This camber orientation necessitates a range of blade rotation about the blade axis of approximately 180 degrees.
Each blade in the installed condition is fastened at its base to a driven bevel gear which is captured by a pivot post and capping disc, thereby allowing the blade to rotate in pitch about the post axis. The gear on each blade engages the pinion and is sized to allow clearance with adjacent gears. The manner of fastening the blades to the bevel gear parts allows for convenient installation of the pivot post capping discs and provides for interchangeable selection of blades and easy repair. A rotational stop feature with or without shock-absorbing features is incorporated between each blade gear and capping disc to limit rotation of each blade at the point of optimal efficiency. Discs may be selected from an array of types and stop locations to match the overall required hydrodynamic performance of the device.
While one blade will suffice for purposes of the present invention, two or three are more practical for application to free-stream propulsors/impellers. The blade nominal camber mid-point can be located at the centerline of the blade pitch pivot or in a biased off-center position so as to provide the most appropriate balance of blade forces and torques and particularly to orient the blades in a minimal drag position when not transmitting power. The blade cross-section is approximately similar at both the leading and trailing edges, with appropriate camber and thickness to perform the desired hydrodynamics and structural functions. The blade camber and pitch form is conventionally helical from the hub to tip.
Operation of the subject invention is as follows:
In the forward or reverse thrust mode, the shaft may be driven in either clockwise or counterclockwise direction. As the shaft is engine/motor driven, a blade drag force creates a torque about the shaft and a torque between the pinion and the blade pivot axis. The torque about the drive shaft causes the outer part of the hub assembly to lag behind the shaft sleeve-with-pinion as it rotates on the journal bearing. The torque about the blade pivot axis causes the blade to rotate until it encounters the stop mechanism. To go to another mode wherein the shaft rotates in the opposite sense, such as, for example, reverse versus forward, the opposite motions take place with another stop being appropriately located where blade pitch angle is approximately 180 degrees, or reverse camber, from the previous position.
In the turbine mode, the drive shaft is driven by the propeller. This construction provides for this to take place with the blades positioned in the reverse propulsion sense. Blade force, and related torque about the drive shaft, are in the sense that locate the blades relative to the hub against the reverse propulsion stop. The torque about the drive shaft created by the blades oriented as a turbine, wherein the camber is inverted from forward propulsion, causes the shaft to rotate in the forward propulsion sense. This is inherently accommodated by an electric motor/generator, or "dynamo" -type device.
In the low drag mode, when no power transfer through the drive shaft is desired, the blades may be allowed to "feather". This feature is accomplished by the location of the blade cross-section relative to the blade pivot axis to institute a balance of forces that causes the blade pitch orientation to seek a "neutral" position. No absolute stop mechanism is employed for this feature as this motion is inherent in the baseline construction; however, a detent-type mechanism may be incorporated to prevent blade flutter or pitch angle hunting. Also, the optional incorporation of a brake on the shaft at its inboard end, i.e., in the proximity of the motor/generator, enhances the feathering characteristics of the device.